Diseases caused by reovirus in mammalian hosts are strain-specific: some type 1 viruses are associated with myocarditis, whereas type 3 viruses cause lethal encephalitis. The molecular mechanisms by which genetically similar reovirus strains cause these disparate diseases are not fully understood. However, pathologic hallmarks of these diseases are recapitulated in cell-culture models of reovirus infection. Encephalitis induced by type 3 reovirus correlates with the capacity of the strain to induce apoptosis both in vivo and in cell culture, whereas reovirus-induced myocarditis is associated with the limited capacity of the strain to induce type 1 interferons (IFNs), a family of related antiviral cytokines. Both IFN induction and apoptosis following reovirus infection are linked to innate immune responses dependent on transcription factors IRF-3 and NF-?B. The central hypothesis of the proposed research is that prototype type 1 strain Lang (T1L) encodes an antagonist of innate immune response activation that alters regulation of cellular transcriptional networks that function to establish an antiviral state or induce apoptosis. Three integrated specific aims are proposed to test this hypothesis. In Specific Aim 1, mechanisms for reovirus strain-specific differences in innate immune activation will be defined. The role of capsid stability in the cytoplasmic exposure of genomic dsRNA, a known inducer of innate immune responses, will be assessed using viruses with known capsid-destabilizing mutations. The genetic basis for these differences will be assessed using single-gene reovirus reassortants generated by reverse genetics. In Specific Aim 2, cellular transcriptional networks responsible for a) apoptosis and b) antiviral signaling will be defined by microarray analysis, using virus reassortants incapable of activating one or both pathways. Specific Aim 3 will facilitate the other two aims and enhance the undergraduate research program at Colgate University by introducing a laboratory component to an elective Virology course, which will engage students in a semester-long project to generate and characterize reovirus reassortants, and by supporting a senior-level research course in which students conduct the independent research projects outlined in Specific Aims 1 and 2. Broadly, this research will enhance understanding of how genetically similar viruses can cause disparate diseases through manipulation of innate immune pathways. The proposed experiments also will provide insight into two long-standing questions in the dsRNA virus field: mechanisms of reovirus-induced apoptosis and mechanisms by which reovirus engages and counteracts cellular antiviral responses. As other pathogenic microbes employ similar strategies, this research program will uncover conserved mechanisms of infectious disease pathogenesis. PUBLIC HEALTH RELEVANCE: Genetically similar viruses can cause widely disparate diseases through manipulation of innate immune pathways. This project uses mammalian reovirus, a powerful experimental model for studies of virus pathogenesis, to identify mechanisms for strain-specific differences in cellular responses to infection that influence organ-specific disease. As other pathogenic microbes employ similar strategies, this research program will uncover conserved mechanisms of infectious disease pathogenesis.